Catadioptric telephoto objective systems



350-444 SR 1/ SEARCH ROOM Jan. 17, 1956 F. G. BACK ETAL 2,730,926

' CATADIOPTRIC TELEPHOTO OBJECTIVE SYSTEMS T2 0 2 Filed Aug. 25, 1954 l l E x l f I I l l5 ELEMENT I GLASS RADII THICKNESSO- SEPARATION CORRECTION PLATE Dense Flini I =-25.047 oInclSECONDARY MIRROR N =L623; V=36.0 R |4.787 20o s=4 ll Borosiiicode Crown R 9.IH PRIMARY MIRROR a I=o.39

N,=I.5Is; V=64.4 Rfl4.074" 5 a I' I R +l4787" SFLSOO BorosIIcc e Crown FIRST REAR EL M NT I:

E E N,,=I.5I6-. v=64.4 R 4.400 3 0230 R H D Fl I R 32165" $50500 ense m SECOND REAR ELEMENT 'I= N =|.62O;V=36.3 R =8.66I 4 0250 Second Rear Elemenf #0 Focal Plane s, =5.507"

Equivalen F'ocoIl LengHI 2Oinche5 Reloliive Aperiure F255 A I N =|ndex of Refrolcfion for Yellow Lz hI (5893A) X4" glllla-r?" jf g, Abbe's Dispersion Number R= Radius of CurvcIIure of Lens Surface CA' IADIOPTRIC TELEPHOTO OBJECTIVE SYSTEMS 2,730,926 Patented Jan. 17, 1956 2 except as limited by the prior art and the scope of the appended claims:

In the drawings- Fig. 1 is a schematic cross-sectional view of one em- M Back and Herbert Lowe, Glen Cove, Y, 6 bodiment of the present invention and shows a lens of 20 equivalent focal length. Applicflfioll August 1954 Sena] 452,136 Fig. 2 is a table of data as they apply to the 20" catadi- 3 Claims. (Cl. -optric telephoto system, illustrated in Fig. l. Telephoto lenses commonly consist of a positive front F Present mventmn relates to oPtleal systems 10 component and a negative rear component. Having now parqcularly to such Systems e genemany ,caued f reference to Fig. 1, it will be seen that the positive front elfme telePhoto System53 whleh are used connecilon component of a telephoto system constructed in accordwlth smleameras y -q a e ance with the present invention consists of a correction cameras and all such other devices in which ob ectives plate 10, of positive power, a meniscus lensmhmr comhh Wlth Y fecal length e e l5 nation 11 which consists of the retracting member 11a It is an ob ect of the present invention to provide such and the reflecting rear surface of Said refracfing objectives of long equivalent focal length, which have a member. The reflecting member 11b serves as the high degree of correction for all aberrations over a large mary mirror of the positive from component The fifild, Whlle at the same tune the P as sueh is of rela' center rear portion of the convex side of the correction llvelX short 8 and llght f g 20 plate 10 is mirrored and forms the secondary mirror of It a further obleet of the Present mvenloni to the positive front component. The negative rear com- P e and novel eonstmetlon such ponent may be constituted of any lens combination of ebleetwes of 9 8 eqelvaleet fecal lengfl} Wherem the combined negative power such as negative lens 13a and flange focal distance is maintained sufiiciently long so Positive lens h as P the use'ef fl e View e and foeesmg The ray-path in the catadioptric telephoto system illusdevices with the said ob ectives despite the relatively trated in Fig 1 is as fouows; short over-all length of the unit. The image forming axial parallel rays pass from the @qvemwnal arrangements of type mmol" object through the correction plate 10 which is of positive ebleeuves when corrected Spheneal aberratlon, tenfi power; thence onto the meniscus lens mirror combination to presentthe effect of anegative non-fulfillment of Abbes 11 by passing through the reh-actihg member 11a and sine condition when they are adequately corrected for impinging upon the spherical, concave primary mirror spherical abemuen- In lenses of low relatlve aperture of the systems positive front component, which is formed F 8 less) {hese efiefits can be e e by by the mirrored rear surface 11b of the meniscus lens; "(many gmroducmssphencalaberraqon m order thence the rays are reflected by said primary concave s sme eondmen- Thls spheneal aberratlen 15 not mirror onto the secondary convex mirror 12 of the system obleeuonable at a speed of or w at which is formed by the mirrored, convex, rear center area speeds greater than F spheneal aberrauons eannot be of the convex side of the correction plate 10; thence the tolerated e aeeoremgly the necessary eol'reenons must rays are reflected by the secondary convex mirror 12 in both ehmmate spherical aberration and the effect of nonsuch manner that the pass through the negative rear fulfillment 9 Abbe S eendltlon- 40 ponent of the telephoto system by traversing the negative The eflielent aecomPhshmeft Such ee eorreeten lens 13a and the positive lens 13b which are of a comfor 1 fulfillment Abbes common and for bined negative power; thence the rays pass through the iphengal conecnon 1s a further object of the present aperture 14 provided within the center portion of the invention.

Other advantages and objects of the present invention i i lens mmor combmauon 11 onto the focal will be obvious on hand of the detailed description of a p E f t I d 2 in b preferred example embodying the invention, and illusavmg 9 re Hence 0 F w e trated in the accompanying drawihgs seen that Fig. 1 represents a catadioptric telephoto sys- It will be understood that for the purpose of adequate tem Yvhleh has an equlvalent focal length of 20 and a and complete description of all the features of the present 0 l'elatlve p r re of a Speed F:5.6. The values for the invention, a preferred example has been illustrated with 5 Components of a catadloptl'lc telephow system as 111118- out thereby limiting the scope of the present invention, trated in Fig. 1, are as follows:

Element Glass Radii Thickness Separation Correction Plate 10, Secondary DF Ri==-25.o47" Mirror 12 hing-61662.3 R 14 787 ti=.500"

1= 8i=4.200" Meniscus Lens, Primary Mirror BSO Ri==-9.111"

ii ND=L51B z,=.a95"

V=e4.4 Ila-14.074"

8i=1.500 Bsc R =+14.787 First Reai-Elementllia goal-4518 R 4400 i:=-230" DF R1=32.165 Second Reai-Elementliib Nn-L620 ti=.250"

V==36.3 Rl= 8.661" Second Rear Element to Focal Plane ei-Mm" Equivalent local length 20. Relative aperture F/6.6. Nn=Index oi refraction for yellow light 6893A.) V -Abbe's dispersion number.

R Radius of curvature of lens surface. B Boro silicate crown.

It will be obvious from the foregoing detailed description of one of the preferred examples of the present invention that the achievement of an improved catadioptric telephoto lens construction is, according to the present invention, accomplished by employing mirror elements in the positive front component and a combination of a refleeting and a refracting element to serve as the primary mirror of the positive front component of the system. The use of a meniscus lens, the rear surface of which is mirrored and reflecting, as primary mirror constitutes an optical means which both reflects and refracts and thus actually may affect an impinging ray three times.

It is obvious that various modifications may be made in the choice of elements, their design and selection by those skilled in the art, without thereby departing from the scope of the present invention, the example having only been specifically detailed to adequately set forth and describe our invention.

Having set forth our invention what we desire to claim and secure by Letters Patent is:

1. In a catadioptric telephoto lens system, a positive, meniscus shaped, positive corrector element concave toward the object space, the center portion of the convex rear-surface thereof adapted to form the secondary mirror of the system, a rear-surface spherical meniscus lens primary mirror positioned behind said corrector plate and said secondary mirror, the front surface of said corrector element having a negative power, said correcting element and said primary mirror forming in combination a substantially corrected positive front component, and a positive lens and a negative lens in spaced axial alignment and of combined negative power forming the negative rear-element of said catadioptric telephoto lens, whereby an image is focused by said lens system at a point behind the rear surface of said primary mirror.

2. In a catadioptric telephoto lens in accordance with claim 1, a positive meniscus shaped corrector plate concave toward the object space, the center portion of the convex rear thereof adapted to form the secondary mirror of the system wherein the dioptric power of said corrector plate is at least A but not more than A of the total power of the whole system and where the absolute value of the negative catoptric power of said convex rear surface is not less than 2 times but not more than 4 times the total power of the system, a rear surface primary mirror at a distance of not less than A; nor more than A of the focal length of the whole system behind said corrector plate and secondary mirror, the front surface of said primary mirror having a negative dioptric power at least but not more than 2 times the absolute power of the whole system, the silvered rearsurface of said primary mirror having a catoptric power of not less than 2 times nor more than 4 ror having a total positive power of not less than 1% times nor more than 3 times the power of the total system, said elements forming in combination a substantially corrected positive front component and a positive and negative lens of a combined negative power of at least A, but not more than of the absolute power of the total system positioned at least $5 but not more than 5 of the total focal length of the system behind the rear surface of said corrector plate and secondary mirror and forming the negative rear element of said telephoto lens.

3. In a catadioptric telephoto system in accordance with claim 1 a lens arrangement comprising:

Wherein the equivalent focal length is 20";

The relative aperature is f/5.6; and

Nn=Index of refraction for Yellow Light (.5893A) V=Abbe's dispersion number.

R= Radius of curvature of lens surface. BSC=B0ro silicate crown.

T=Thickness of lens.

S=Airspece between elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,239,538 Richter Apr. 22, 1941 2,504,383 Bouwers Apr. 18, 1950 2,701,983 Back et al. Feb. 15, 1955 FOREIGN PATENTS 724,026 Germany Aug. 15, 1942 824,558 Germany Dec. 13, 1951 969,797 France May 31, 1950 OTHER REFERENCES Maksutov: Article, New Catadioptric Meniscus Sys tems, pages 270-284, Journal Optical Society of America. vol. 34, No. 5, May 1944, pages 278 and 279 cited. 

